In the case of water environment such as a pond or a fish tank, its close interconnection with the atmospheric air is essential both to ensure the required amount of oxygen in the water and to prevent a deep deficiency or, the opposite, excessive accumulation of carbon dioxide. The deficiency of carbon dioxide in water reservoirs may occur in conditions of exposure to light during intensive vegetation growth, resulting, among other things, in intensive alkalization of water; whereas the accumulation of CO2 excess may occur at night or due to undesirable excessive fertilization of water with carbon dioxide, which may cause the death of the entire population of fish. Regulation of the concentration of gases such as oxygen or air by means of a thorough aeration of water, as well as regulation of carbon dioxide concentration effectively prevent damage to water environment. Moreover, motion of water caused by diffusing gas bubbles ensures highly favourable, mild, but massive, mixing of the entire water volume. An additional benefit is the acceleration of the process of removal of harmful gases from water. In the case of a fish tank, any columns, draperies or clouds of silvery or white air bubbles hovering in the water (with pulsing pump operation) and constituting an additional, decorative element is not without significance.
Diffusers available on the market, used, for example, for aeration of water, can be divided into several groups. The first one are diffusers made of natural sandstone by carving, usually of a rectangular cuboid shape with rounded edges, with a drilled hole in it, and with a connector pipe connected to a gas entry tube attached to it. The gas introduced into the cuboid penetrates the gaps between the grains of sandstone and is driven out into the water in the form of bubbles.
Another type of diffusers comprise ceramic or glass elements made by sintering small grains of quartz, glass or other materials into a form of a specific shape. This form has a hole equipped with a connector pipe attached to a gas entry tube. Like in the sandstone diffusers, the gas penetrates the spaces between the melted grains and is driven outwards, into the water.
A further type of diffusers is a wooden rectangular cuboid, usually made of lime wood, with a hole in one of the walls (usually the shorter one), equipped with a connector pipe attached to a gas entry tube. The gas introduced into the cuboid interior penetrates the wood along its pores and is driven outwards into the water, usually only through two out of four bigger walls (due to orientation of the tubular pores forming the structure of the wood).
Another group are diffusers made of plastics, produced as a result of perforation of at least one wall of a synthetic element, e.g. a plastic chamber or a tube. In this case, gas introduced into the interior of the element is driven outwards into the water environment through the perforation.
A common feature of the aforementioned diffusers is a big ratio of their total area impenetrable by a gas to the total area of gaps through which the gas may be driven outwards. In all cases, with the exception of a lime wood cuboid, the volume of grains forming the diffuser is much greater than the volume of the gaps between them, the gaps being neither tube-shaped nor oriented. In the case of the lime wood cuboid, the gaps are oriented along the tubular pores forming the structure of the wood, however, the total volume of organic material impenetrable by gas is much greater than the total volume of gaps.